(3aR,6aS)-1-(tert-butoxycarbonyl)octahydrocyclopenta[c]pyrrol-2-iuM carboxyfor

540-88-5

1205676-44-3

144-62-7

907606-68-2

[Isolation of hydroxyoxalate] To a mixture of 250 mg of (1S,3aR,6aS)-octahydrocyclopenta[c]pyrrole-1-carboxylic acid hydrochloride (i) and the ammonium chloride prepared in Example 29 was added 4 mL of chloroform and 1.7 mL of tert-butyl acetate. The resulting suspension was cooled to 0°C and then 0.25 mL of methanesulfonic acid was added. The mixture was slowly warmed to 25°C and stirred at this temperature for 18 hours. The resulting white suspension was again cooled to 0°C, and then 1.3 mL of 50% aqueous sodium hydroxide was slowly added while controlling the temperature to not exceed 20°C. 15 mL of water and 15 mL of chloroform were added and stirred for 15 minutes. The organic and aqueous layers were separated and the aqueous layer was extracted three times with 15 mL of chloroform. The organic layers were combined, dried with magnesium sulfate, filtered and the solvent concentrated under reduced pressure. To the light green residue was added 2.5 mL of tert-butyl acetate and 146.7 mg of oxalic acid in a 2.5 mL 2-propanol solution. The mixture was heated to 75-80 °C, stirred for 30 minutes, cooled to room temperature (about 20 °C), continued stirring for 18 hours, and then filtered. The resulting solid was washed sequentially with 5 mL of 2-propanol and 5 mL of methyl tert-butyl ether, and dried to give 0.08 g (0.27 mmol, 25% overall yield based on nitrile (h)) of tert-butyl (1S,3aR,6aS)-octahydrocyclopenta[c]pyrrole-1-carboxylate oxalate (j) as a white solid.